You query is correct. However, the problem here is the value you saved for date has the format "dd/mm/yyyy" which will cause the incorrect order when sorting. I suggest you use "yyyy-mm-dd" format, which is safe when ordering.
If so, you can set the timestamp parameter for the field true. This will make the field save the timestamp instead of date string, so you can sort by that, while still display in the correct format to users.